1. Field of the Invention
The present invention relates to an elevating apparatus for lifting workers and materials to a higher place and lowering unwanted materials.
2. Description of the Prior Art
There have heretofore been used elevating apparatus for elevating a lifting table to lift workers and/or materials to higher places for assembly, painting, repair in various locations such as construction sites, highways, and other areas requiring work at elevated levels. Such elevating apparatus include boom-type lifts and scissors-type lifts. The boom-type lift includes a plurality of booms telescopically assembled together. The boom-type lift can move a bucket to a higher place by increasing the number of telescopically assembled booms. However, the booms would tend to be bent if the length thereof were unduly increased. Another disadvantage with the boom-type lift is that it cannot lift heavy objects. The scissors-type lift is in the form of a pantograph comprising X-shaped arms which are vertically connected. In each of the X-shaped arm structure, two arms are centrally pivotally interconnected. The scissors-type lift can lift relatively heavy objects. However, in order to raise a platform to a higher location, each of the arms has to be increased in length or the number of X-shaped arm units has to be increased. This has led to problems in that the platform is liable to swing at an elevated level, and the arms as they are folded have an increased height from the ground, making it tedious and time-consuming for workers and materials to be placed on and off the platform.
To cope with the foregoing difficulties, there has been proposed an elevating mechanism in which a plurality of booms are telescopically inserted in one arm so that the arm can be longitudinally expanded (see for example Japanese Patent Applications Nos. 56-134487 and 56-191065). FIG. 1 of the accompanying drawings illustrates the proposed elevating mechanism. Hollow middle booms A, B are centrally interconnected by a shaft C in the form of an X, the booms A, B being angularly movable about the shaft C. Upper and lower booms D, E and F, G are telescopically disposed in the middle booms A, B and movable in and out of open ends thereof. A platform I is coupled to the upper booms D, E, and the lower booms F, G are connected to a base H. When the shaft c is moved upwardly by a hydraulic cylinder (not shown), the upper and lower booms D, E and F, G are drawn out of the open ends of the middle booms A, B to raise the platform I away from the base H. In order that the platform I will be vertically moved away from the base H, the upper and lower booms D, E and F, G have to be drawn out of the open ends of the middle booms A, B by the same distances L, and a synchronizing mechanism is required to control the intervals of movement of the upper and lower booms D, E and F, G. Although it is relatively easy to synchronize the upper and lower booms D, F or the upper and lower booms E, G, synchronization of the upper booms D, E requires a complex and large synchronizing mechanism because of the pivotal movement around the shaft C. If all of the upper and lower booms D, E and F, G are synchronized, then the platform I will be lifted and lowered only vertically, but in no other directions such as a horizontal direction. However, in actual use, the platform I may be required to move horizontally toward a desired location after it has been vertically lifted.